Temperature sensing circuit and electronic device using same

ABSTRACT

A temperature sensing circuit that detects a given temperature includes a first differential input circuit and a second differential input circuit connected to the first differential input circuit. The first differential input circuit is configured to provide a first offset voltage with no temperature coefficient. The second differential input circuit is configured to provide a second offset voltage with a non-zero temperature coefficient. The given temperature is detected based on the first offset voltage and the second offset voltage. An electronic device using such a temperature sensing circuit is also disclosed.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a temperature sensing circuit, and moreparticularly, to a temperature sensing circuit that detects temperaturebased on a difference in gate work function between multipletransistors, and electronic devices, such as voltage regulators,personal computers, portable devices, and home appliances, using such atemperature sensing circuit.

2. Discussion of the Background

Temperature sensing circuits are used in various electronic devices,such as voltage regulators, personal computers, and various kinds ofportable devices and home appliances, where control is performed inresponse to changes in ambient temperature.

FIG. 1 is a diagram illustrating an example of a conventionaltemperature sensing circuit.

As shown in FIG. 1, the conventional circuit includes a comparator 30, areference voltage Vr, diodes D1 and D2, and a constant current sourceI1.

In the temperature sensing circuit, the constant current source I1 andthe diodes D1 and D2 are connected in series between a voltage sourceVdd and ground, forming a node N1 between the current source I1 and thediode D1. The comparator 30 has a non-inverting input connected to thenode N1, an inverting input connected to the reference voltage Vr, andan output to provide a temperature detection signal Out.

During operation, the comparator 30 compares a voltage drop across thediodes D1 and D2 against the reference voltage Vr. The voltage Vr isgenerated by an appropriate source (e.g., a bandgap regulator) having agood temperature coefficient. The comparator output Out switchesaccording to whether the voltage drop is above or below the referencevoltage Vr.

The above temperature sensing circuit is designed to take advantage ofthe fact that the voltage drop across the series diodes D1 and D2 biasedwith the constant current I1 has a temperature coefficient. However,such a conventional design involves various electronic components forimplementing various functions, such as pn junction diodes for theseries diodes D1 and D2, a voltage regulator for the reference voltagesource Vr, and other elements for the comparator 30, leading toincreased size and complexity of the temperature sensing circuit.

By contrast, instead of using a voltage drop across coupled diodes, somerecent techniques provide temperature sensing capabilities through useof a difference in gate work function between metal-oxide-semiconductorfield-effect transistors (MOSFETs) with a controlled temperaturecoefficient.

FIG. 2 is a block diagram schematically illustrating an example of sucha temperature sensing circuit.

As shown in FIG. 2, the temperature sensing circuit includes a firstvoltage generator 101, a second voltage generator 102, a subtractor 103,and a comparator 104.

The first voltage generator 101 generates a voltage Svptat proportionalto absolute temperature (PTAT) and hence having a linear temperaturecoefficient either positive or negative. The second voltage generator102 generates a first reference voltage Vref, a second reference voltageTvref, and a third reference voltage Svref, all having no temperaturecoefficient.

The subtractor 103 amplifies a difference between the voltage Svptat andthe third reference voltage Svref to provide an output Tvptat to thecomparator 104. The comparator 104 then compares the signal Tvptatagainst the second reference voltage Tvref to output a temperaturedetection signal Tout.

In such a configuration, the second voltage generator 102 providing avoltage with no temperature coefficient operates based on a differencein gate work function between multiple FETs.

FIG. 3 is a diagram illustrating still another example of temperaturesensing circuit.

As shown in FIG. 3, the temperature sensing circuit includes a firstvoltage generator 201, a second voltage generator 202, an impedancetransformer 203, and a subtractor 204.

The first voltage generator 201 generates an output voltage VPN with anegative temperature coefficient based on a difference in gate workfunction between a pair of FETs.

The second voltage generator 202 generates a reference voltage VREF1with no temperature coefficient based on a difference in gate workfunction between multiple FETs.

The impedance transformer 203 includes first and second operationalamplifiers (op-amps) AMP1 and AMP2, and performs impedancetransformation on the signals VPN and VREF1 prior to transmission to thesubtractor 204.

In the impedance transformer 203, the first and second op-amps AMP1 andAMP2 each forms a voltage follower with an output connected to aninverting input. The first op-amp AMP1 receives the voltage VPN at anon-inverting input and provides a low-impedance output to one inputterminal of the subtractor 204. Similarly, the second op-amp AMP2receives the voltage VREF1 at a non-inverting input and provides alow-impedance output to another input terminal of the subtractor 204.

The subtractor 204 includes an op-amp AMP and resistors R1 through R4,and provides a temperature detection signal VOUT at an output of theop-amp AMP.

In the subtractor 204, the op-amp AMP receives the reference voltageVREF1 at a non-inverting input via the resistor R1 and the voltage VPNat an inverting input via the resistor R3, with the resistor R2connected between the non-inverting input and ground, and the resistorR4 connected between the output and inverting input. The temperaturedetection signal VOUT is generated through subtraction between the inputvoltages VREF1 and VPN.

In such a configuration, a voltage VREF1-VPN obtained by subtracting thenegative-temperature-coefficient voltage VPN from theno-temperature-coefficient voltage VREF1 has a positive temperaturecoefficient. Thus, the detection signal VOUT obtained by amplifyingVRFF1-VPN also has a positive temperature coefficient greater than thatof the difference voltage VRFF1-VPN, which provides good detectionaccuracy and low energy consumption of the temperature sensing circuit.

Although providing temperature sensing capabilities without usingdiodes, the MOSFET-based approaches illustrated in FIGS. 2 and 3 do notprovide a satisfactory reduction in circuit size, since these circuitsrequire two voltage generators, one with a temperature coefficient andthe other with no temperature coefficient, in addition to a comparatorfor comparing the outputs of the voltage generators.

Accordingly, there remains a need for a temperature sensing circuit thatprovides a good temperature detection performance in a simple andcompact circuit configuration. Such a circuit will contribute to a sizereduction of various electronic devices incorporating temperaturesensing capabilities.

BRIEF SUMMARY

This disclosure describes a novel temperature sensing circuit based on adifference in gate work function between multiple transistors.

In one aspect of the disclosure, the novel temperature sensing circuitthat detects a given temperature includes a first differential inputcircuit and a second differential input circuit connected to the firstdifferential input circuit. The first differential input circuit isconfigured to provide a first offset voltage with no temperaturecoefficient. The second differential input circuit is configured toprovide a second offset voltage with a non-zero temperature coefficient.The given temperature is detected based on the first offset voltage andthe second offset voltage.

This disclosure also describes a novel electronic device incorporatingthe temperature sensing circuit described above.

In one aspect of the disclosure, the novel electronic device includes atemperature sensing circuit that detects a given temperature. Thetemperature sensing circuit includes a first differential input circuitand a second differential input circuit connected to the firstdifferential input circuit. The first differential input circuit isconfigured to provide a first offset voltage with no temperaturecoefficient. The second differential input circuit is configured toprovide a second offset voltage with a non-zero temperature coefficient.The given temperature is detected based on the first offset voltage andthe second offset voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating an example of a conventionaltemperature sensing circuit;

FIG. 2 is a block diagram schematically illustrating an example ofanother conventional temperature sensing circuit;

FIG. 3 is a diagram illustrating an example of still anotherconventional temperature sensing circuit;

FIG. 4A is a diagram illustrating an embodiment of a temperature sensingcircuit according to this patent specification;

FIGS. 4B and 4C are circuit diagrams of an operational amplifier and acomparator, respectively, used in the temperature sensing circuit ofFIG. 4A;

FIG. 5 shows voltage plotted against temperature, illustrating operationof the temperature sensing circuit of FIG. 4A;

FIG. 6 is a diagram illustrating another embodiment of the temperaturesensing circuit;

FIG. 7 shows voltage plotted against temperature, illustrating operationof the temperature sensing circuit of FIG. 6;

FIG. 8 is a diagram illustrating still another embodiment of thetemperature sensing circuit;

FIG. 9 shows voltage plotted against temperature, illustrating operationof the temperature sensing circuit of FIG. 8;

FIG. 10 is a diagram illustrating still another embodiment of thetemperature sensing circuit;

FIG. 11 shows voltage plotted against temperature, illustratingoperation of the temperature sensing circuit of FIG. 10;

FIG. 12 is a diagram illustrating still another embodiment of thetemperature sensing circuit;

FIG. 13 shows voltage plotted against temperature, illustratingoperation of the temperature sensing circuit of FIG. 12;

FIG. 14 is a diagram illustrating still another embodiment of thetemperature sensing circuit;

FIG. 15 shows voltage plotted against temperature, illustratingoperation of the temperature sensing circuit of FIG. 14; and

FIG. 16 is a diagram illustrating in detail the temperature sensingcircuit of FIG. 6.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In describing exemplary embodiments illustrated in the drawings,specific terminology is employed for the sake of clarity. However, thedisclosure of this patent specification is not intended to be limited tothe specific terminology so selected, and it is to be understood thateach specific element includes all technical equivalents that operate ina similar manner and achieve a similar result. Referring now to thedrawings, wherein like reference numerals designate identical orcorresponding parts throughout the several views, examples and exemplaryembodiments of this disclosure are described.

FIG. 4A is a diagram illustrating an embodiment of a temperature sensingcircuit 1 according to this patent specification.

As shown in FIG. 4A, the temperature sensing circuit 1 includes anoperational amplifier or op-amp 10 and a comparator 20.

The op-amp 10 includes a first differential input circuit Sd1 in aninput stage with an inverting input positive with respect to anon-inverting input. The first differential input circuit Sd1 provides afirst offset voltage Vo1 having no temperature coefficient.

The op-amp 10 has an output connected to the inverting input to form avoltage follower. With the non-inverting input connected to ground, theoutput of the op-amp 10 is equal to the first offset voltage Vo1.

The comparator 20 includes a second differential input circuit Sd2 in aninput stage with an inverting input positive with respect to anon-inverting input. The second differential input circuit Sd2 providesa second offset voltage Vo2 having a negative temperature coefficient.

The comparator 20 has the inverting input connected to the output of theop-amp 10 and the non-inverting input connected to ground. Throughcomparison of the inverting and non-inverting inputs, the comparator 20outputs a temperature detection signal Out indicating when temperaturereaches a given set-point Ts.

FIGS. 4B and 4C are circuit diagrams of the op-amp 10 and the comparator20 used in the temperature sensing circuit 1 of FIG. 4A.

As shown in FIGS. 4B and 4C, the op-amp 10 and the comparator 20 bothare built based on a combination of metal-oxide-semiconductorfield-effect transistors (MOSFETs), a detailed description of which willbe given with reference to FIG. 16.

FIG. 5 shows the voltages Vo1 and Vo2 plotted against temperature,illustrating operation of the temperature sensing circuit 1 of FIG. 4Anear the set temperature Ts.

As shown in FIG. 5, the first offset voltage Vo1 or the output of theop-amp 10 does not vary with temperature due to having no temperaturecoefficient, while the second offset voltage Vo2 or the input stagevoltage of the comparator 20 decreases with increasing temperature dueto having a negative temperature coefficient.

Specifically, the voltage Vo2 remains higher than the voltage Vo1 attemperatures below the set-point Ts, matches Vo1 at the set-point Ts,and falls below Vo1 when temperature exceeds the set-point Ts.

Thus, the temperature detection signal Out output by the comparator 20,which is high for Vo2>Vo1 and low for Vo2<Vo1, switches at the set-pointTs.

FIG. 6 is a diagram illustrating another embodiment of the temperaturesensing circuit 1.

As shown in FIG. 6, this embodiment is similar to that depicted in FIG.4A, except that the temperature sensing circuit 1 includes resistors R1and R2 forming a voltage divider to divide the op-amp output Vo1 so thatthe comparator 20 receives a scaled voltage VA at the inverting input.

FIG. 7 shows the voltages Vo1, Vo2, and VA plotted against temperature,illustrating operation of the temperature sensing circuit 1 of FIG. 6near the set temperature Ts.

As shown in FIG. 7, the inverting input VA of the comparator, obtainedfrom the temperature-independent voltage Vo1, does not vary withtemperature, while the temperature-dependent voltage Vo2 decreases withincreasing temperature. The temperature detection signal Out output bythe comparator 20 is high for Vo2>VA and low for Vo2<VA, switching atthe set-point Ts.

FIG. 8 is a diagram illustrating still another embodiment of thetemperature sensing circuit 1.

As shown in FIG. 8, this embodiment is similar to that depicted in FIG.4A, except that the op-amp 10 is provided with a resistor R3 interposedbetween its inverting input and output and a resistor R4 between itsinverting input and ground, so as to have a gain of 1+R3/R4 instead offorming a voltage follower.

FIG. 9 shows the voltages Vo1, Vo2, and VA plotted against temperature,illustrating operation of the temperature sensing circuit 1 of FIG. 8near the-set temperature Ts.

As shown in FIG. 9, the inverting input VA of the comparator, obtainedfrom the temperature-independent voltage Vo1, does not vary withtemperature, while the temperature-dependent voltage Vo2 decreases withincreasing temperature. The temperature detection signal Out output bythe comparator 20 is high for Vo2>VA and low for Vo2<VA, switching atthe set-point Ts.

FIG. 10 is a diagram illustrating still another embodiment of thetemperature sensing circuit 1.

As shown in FIG. 10, this embodiment is similar to that depicted in FIG.4A, except that the second differential input circuit Sd2 withtemperature coefficient is included in the input stage of the op-amp 10,and the first differential input circuit Sd1 with no temperaturecoefficient is included in the input stage of the comparator 20.

FIG. 11 shows the voltages Vo1, Vo2, and VA plotted against temperature,illustrating operation of the temperature sensing circuit 1 of FIG. 10near the set temperature Ts.

As shown in FIG. 11, the first offset voltage Vo1 or the input stagevoltage of the comparator 20 does not vary with temperature due tohaving no temperature coefficient, while the second offset voltage Vo2or the output of the op-amp 10 decreases with increasing temperature dueto having a negative temperature coefficient.

As a result, the temperature detection signal Out output by thecomparator 20, which is low for Vo2>Vo1 and high for Vo2<Vo1, switchesat the set-point Ts.

FIG. 12 is a diagram illustrating another embodiment of the temperaturesensing circuit 1.

As shown in FIG. 12, this embodiment is similar to that depicted in FIG.10, except that the temperature sensing circuit 1 includes resistors R1and R2 forming a voltage divider to divide the op-amp output Vo1 so thatthe comparator 20 receives a scaled voltage VA at the inverting input.

FIG. 13 shows the voltages Vo1, Vo2, and VA plotted against temperature,illustrating operation of the temperature sensing circuit 1 of FIG. 12near the set temperature Ts.

As shown in FIG. 13, the inverting input VA of the comparator 20,obtained from the temperature-dependent voltage Vo2, decreases withincreasing temperature, while the temperature-independent voltage Vo1does not vary with temperature. The temperature detection signal Outoutput by the comparator 20 is low for VA>Vo1 and high for VA<Vo1,switching at the set-point Ts.

FIG. 14 is a diagram illustrating still another embodiment of thetemperature sensing circuit 1.

As shown in FIG. 14, this embodiment is similar to that depicted in FIG.10, except that the op-amp 10 is provided with a resistor R3 interposedbetween its inverting input and output and a resistor R4 between itsinverting input and ground, so as to have a gain of 1+R3/R4 instead offorming a voltage follower.

FIG. 15 shows the voltages Vo1, Vo2, and VA plotted against temperature,illustrating operation of the temperature sensing circuit 1 of FIG. 14near the set temperature Ts.

As shown in FIG. 15, the inverting input VA of the comparator 20,obtained from the temperature-dependent voltage Vo2, decreases withincreasing temperature, while the temperature-independent voltage Vo1does not vary with temperature. The temperature detection signal Outoutput by the comparator 20 is low for VA>Vo1 and high for VA<Vo1,switching at the set-point Ts.

In the temperature sensing circuit 1 described above, the firstdifferential input circuit Sd1 providing the offset voltage Vo1 withzero temperature coefficient and the second differential input circuitSd2 providing the offset voltage Vo2 with temperature coefficient areincluded in the input stages of the op-amp 10 and the comparator 20,respectively. As the comparator 20 incorporates the capabilities of areference voltage generator and a temperature-dependent voltage source,which are required to construct a temperature sensing circuit, a compactcircuit configuration is achieved without involving complicatedelectronic components.

Further, the zero-temperature coefficient circuit Sd1 and thetemperature-dependent circuit Sd2 each can be used as the input stage ofeither the op-amp 10 or the comparator 20 as shown in the illustratedembodiments, where the temperature coefficient is present in thecomparator 20 and not in the op-amp 10 for the embodiments of FIGS. 4A,6, and 8, and vice versa for the embodiments of FIGS. 10, 12, and 14.Such interchangeability of the differential input circuits Sd1 and Sd2allows for wide variations in the design of the temperature sensingcircuit 1.

Still further, the temperature sensing circuit 1 can assume variousconfigurations of the op-amp 10, such as those having high gain oramplification, those having unity gain (i.e., the voltage follower), orthose having resistors to divide the output voltage, which offersflexibility to respond to variations in the magnitude and/or temperaturecoefficient of the offset voltages Vo1 and Vo2.

Additionally, although the non-inverting input of the op-amp 10 and thereference input of the comparator 20 are grounded in the illustratedembodiments, these terminals may be connected to an appropriate voltageother than ground potential. In the embodiments using a pair ofresistors to amplify or divide the op-amp output, i.e., the voltagedivider R1 and R2 or the gain resistors R3 and R4, a higher accuracy intemperature detection may be obtained by tuning resistance of one orboth of the paired resistors through trimming or the like.

Referring now to FIG. 16, a diagram illustrating in detail thetemperature sensing circuit 1 according to the embodiment of FIG. 6 isdepicted.

As shown in FIG. 16, the op-amp 10 includes depletion-type n-channel MOS(NMOS) transistors M11 and M12, NMOS transistors M13 and M17, andp-channel MOS (PMOS) transistors M14 through M16, each having MOSFETgate, source, and drain terminals.

The depletion-type NMOS transistors M11 and M12 form the firstdifferential input circuit Sd1 in the input stage of the op-amp 10,where the gate of the NMOS transistor M11 serves as the inverting inputand the gate of the NMOS transistor M12 serves as the non-invertinginput.

The sources of the input transistors M11 and M12 are connected in commonto the drain of the NMOS transistor M13. The NMOS transistor M13 has itssource connected to ground and its gate connected to a bias voltageVbias.

The drain of the NMOS transistor M11 is connected to the drain of thePMOS transistor M14, and the drain of the NMOS transistor M12 isconnected to the drain of the PMOS transistor M15.

The PMOS transistors M14 and M15 have their sources connected in commonto a voltage source Vdd and their gates connected in common to the drainof the PMOS transistor M14 to form a current mirror, which acts as aload in the differential input circuit Sd1.

The drain of the NMOS transistor M12 is connected to the gate of thePMOS transistor M16. The PMOS transistor M16 has its source connected tothe voltage source Vdd and its drain connected to the drain of the NMOStransistor 17. The NMOS transistor M17 has its source connected toground and its gate connected to the bias voltage Vbias in common withthe gate of the NMOS transistor M13.

The op-amp 10 derives an output voltage from the drain of the PMOStransistor M16. As mentioned, the op-amp 10 forms a voltage followerwith the inverting input, i.e., the gate of the NMOS transistor M11,connected to the output voltage. With its non-inverting input, i.e., thegate of the NMOS transistor M12, connected to ground, the op-amp 10provides the output voltage equal to the offset voltage Vo1 of thedifferential input circuit Sd1.

In such a configuration, the offset voltage Vo1 results from adifference in threshold voltage between the input transistors M11 andM12.

In general, threshold voltage of a MOS transistor may be adjusted bydoping, i.e., by implanting impurities called dopants of a particularconductivity type, to change work function of the gate terminal, where ap-type doped (P+) gate has a relatively high threshold voltage and ann-type doped (N+) gate has a relatively low threshold voltage.

In the differential input circuit Sd1, the gate of the transistor M11 isdoped with p-type impurities and the gate of the transistor M12 is dopedwith n-type impurities, so that the transistor M11 has a higherthreshold voltage than that of the transistor M12. Hence, the offsetvoltage Vo1 is obtained with the input transistor M11 having a positivegate potential relative to that of the input transistor M12.

The temperature coefficient of the offset voltage Vo1 thus obtained isdependent on the ratio of size or gate length between the inputtransistors M11 and M12. In the differential input circuit Sd1, the sizeratio of the transistor M11 to the transistor M12 is set toapproximately 2:1 to provide the offset voltage Vo1 with zerotemperature coefficient.

With further reference to FIG. 16, the output terminal of the op-amp 10is connected to the inverting input of the comparator 20 via the voltagedivider resistors R1 and R2.

The comparator 20 includes depletion-type NMOS transistors M21 and M22,an NMOS transistor M23, and PMOS transistors M24 and M25, each havingMOSFET gate, source, and drain terminals.

The depletion-type NMOS transistors M21 and M22 form the seconddifferential input circuit Sd2 in the input stage of the comparator 20,where the gate of the NMOS transistor M21 serves as the inverting inputand the gate of the NMOS transistor M22 serves as the non-invertinginput.

The sources of the input transistors M21 and M22 are connected in commonto the drain of the NMOS transistor M23. The NMOS transistor M23 has itssource connected to ground and its gate connected to a bias voltageVbias.

The drain of the NMOS transistor M21 is connected to the drain of thePMOS transistor M24, and the drain of the NMOS transistor M22 isconnected to the drain of the PMOS transistor M25.

The PMOS transistors M24 and M25 have their sources connected in commonto a voltage source Vdd and their gates connected in common to the drainof the PMOS transistor M25 to form a current mirror, which acts as aload in the differential input circuit Sd2.

The comparator 20 derives the output Out from the drain of the NMOStransistor M21, which switches when the offset voltage Vo2 reaches thelevel of the inverting input.

In such a configuration, as in the case of the first offset voltage Vo1,the offset voltage Vo2 results from a difference in threshold voltagebetween the input transistors M21 and M22, obtained by creating adifference in gate work function.

Specifically, the gate of the transistor M21 is doped with p-typeimpurities and the gate of the transistor M22 is doped with n-typeimpurities, so that the transistor M21 has a higher threshold voltagethan that of the transistor M22. Hence, the offset voltage Vo1 isobtained with the input transistor M21 having a positive gate potentialrelative to that of the input transistor M22.

The offset voltage Vo2 of the differential input circuit Sd2 thusobtained has a negative temperature coefficient, which is created bysetting the size ratio of the transistor M21 to the transistor M22 toapproximately 1:10.

As described above, the differential input circuit according to thispatent specification has an offset voltage controlled by a difference ingate work function between a pair of input transistors, one with a P+doped gate and the other with an N+ doped gate. The size ratio of theinput transistors is adjusted so as to set the temperature coefficientof the offset voltage to zero or any appropriate value positive ornegative.

Through effective use of the differential input circuit, the temperaturesensing circuit 1 according to this patent specification achievesprecise temperature detection with a simple and compact circuitconfiguration.

The temperature sensing circuit 1 may be used in any type of electronicequipment, such as voltage regulators, personal computers, and varioustypes of portable devices and home appliances, where temperature sensingcapability is required to perform a given function in response todetection of a given set-point temperature, such as switching of powerand/or control signals.

Numerous additional modifications and variations of the presentdisclosure are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, thedisclosure of this patent specification may be practiced otherwise thanas specifically described herein.

This patent specification is based on Japanese patent application No.JP-A-2007-233788 filed on Sep. 10, 2007 in the Japanese Patent Office,the entire contents of which are hereby incorporated by referenceherein.

1. A temperature sensing circuit that detects a given temperature, the circuit comprising: a first differential input circuit configured to provide a first offset voltage with no temperature coefficient; and a second differential input circuit connected to the first differential input circuit and configured to provide a second offset voltage with a non-zero temperature coefficient, the given temperature being detected based on the first offset voltage and the second offset voltage.
 2. The temperature sensing circuit according to claim 1, further comprising: an operational amplifier including the first differential input circuit in an input stage thereof; and a comparator including the second differential input circuit in an input stage thereof, the operational amplifier having a non-inverting input connected to a given potential, and an inverting input and an output connected together to form a voltage follower, the comparator having one input connected to the output of the operational amplifier, another input connected to the given potential, and an output providing a signal upon detection of the given temperature.
 3. The temperature sensing circuit according to claim 2, further comprising a voltage divider configured to divide the output of the operational amplifier prior to connection to the one input of the comparator.
 4. The temperature sensing circuit according to claim 2, wherein the given potential is ground.
 5. The temperature sensing circuit according to claim 1, further comprising: an operational amplifier including the first differential input circuit in an input stage thereof; and a comparator including the second differential input circuit in an input stage thereof, the operational amplifier having a non-inverting input connected to a given potential, and configured to multiply the first offset voltage by a given gain, the comparator having one input connected to an output of the operational amplifier, another input connected to the given potential, and an output providing a signal upon detection of the given temperature.
 6. The temperature sensing circuit according to claim 5, wherein the given potential is ground.
 7. The temperature sensing circuit according to claim 1, further comprising: a comparator including the first differential input circuit in an input stage thereof; and an operational amplifier including the second differential input circuit in an input stage thereof, the operational amplifier having a non-inverting input connected to a given potential, and an inverting input and an output connected together to form a voltage follower, the comparator having one input connected to an output of the operational amplifier, another input connected to the given potential, and an output providing a signal upon detection of the given temperature.
 8. The temperature sensing circuit according to claim 7, further comprising a voltage divider configured to divide the output of the operational amplifier prior to connection to the one input of the comparator.
 9. The temperature sensing circuit according to claim 7, wherein the given potential is ground.
 10. The temperature sensing circuit according to claim 1, further comprising: a comparator including the first differential input circuit in an input stage thereof; and an operational amplifier including the second differential input circuit in an input stage thereof, the operational amplifier having a non-inverting input connected to a given potential, and configured to multiply the second offset voltage by a given gain, the comparator having one input connected to an output of the operational amplifier, another input connected to the given potential, and an output providing a signal upon detection of the given temperature.
 11. The temperature sensing circuit according to claim 10, wherein the given potential is ground.
 12. The temperature sensing circuit according to claim 1, wherein each of the first and second differential input circuits is formed by combining first and second transistors having different gate work functions.
 13. The temperature sensing circuit according to claim 12, wherein the first transistor has a p-type doped gate and the second transistor has an n-type doped gate, and the temperature coefficient of each of the first and second differential circuits is adjusted by tuning a size ratio between the p-type doped gate and the n-type doped gate.
 14. An electronic device comprising a temperature sensing circuit configured to detect a given temperature, the circuit including: a first differential input circuit configured to provide a first offset voltage with no temperature coefficient; and a second differential input circuit connected to the first differential input circuit and configured to provide a second offset voltage with a non-zero temperature coefficient, the given temperature being detected based on the first offset voltage and the second offset voltage.
 15. The electronic device according to claim 14, wherein the electronic device is one of a voltage regulator, a personal computer, a portable device, and a home appliance. 